The present invention relates to a ben axis type axial piston machine. More particularly, the present invention pertains to a thrust-radial hydrostatic bearing support type, bent axis type axial piston machine which is suitable for use at high pressures. Still more particularly, the present invention is concerned with a thrust hydrostatic bearing device for use in an axial piston machine which is suitable for carrying out a method of supporting the axial components of piston reaction force loads, relative to a driving shaft, as well as moment loads caused by these axial components.
Known devices of the type described above are designed to support thrust loads by the provision of a hydrostatic shoe for each piston. Such a device is disclosed in, for example, the specification of Japanese Patent Laid-Open No. 131776/1984.
In this piston machine, the number of pistons associated with the discharge pressure varies between certain values and is in accordance with the total number of pistons. For example, if a total of nine pistons is provided, the number of pistons associated with the discharge pressure varies between five and four. Therefore, the resultant force of the piston reaction force loads varies with the number of pistons located in the discharge pressure area and in proportion to the rotational speed of a driving shaft, the path of the point of application thereof generally being described as a figure eight. Due to this dynamic behavior of the piston reaction forces, not only thrust loads but also moment loads act on a drive disc of a driving shaft which supports a plurality of piston rods, the moment loads being supported by hydrostatic shoes. In this case, the moment loads also act on the hydrostatic shoes located in the suction pressure area.
When axes perpendicular to each other and to the axis of the driving shaft are called the x-axis and y-axis, moment loads about the x- and y-axes are exerted alternately on the drive disc in correspondence with the discharge pressure. In the prior art, however, it has not been considered necessary to support such moment loads uniformly by hydrostatic bearings whose pocket pressures are maintained constant. Therefore, the moment loads have been supported by the hydrostatic shoes which are located in the suction area and are incapable of loading static pressures and the hydrostatic shoes which are located in the discharge pressure area and are capable of loading static pressures, resulting in the hydrostatic shoes located on the suction side coming into contact with the body (or a pressure plate mounted on the operation shaft). This makes part of the plurality of hydrostatic shoes contacted with the body while they are rotated, causing unbalanced wear or seizure thereof. Further, since the sliding surface of the drive disk of the operation shaft is tilted with respect to the sliding surfaces of the plurality of hydrostatic shoes at a fixed angle, leakage will increase from these sliding surfaces, increasing the power loss.